1. Technical Field
The present invention relates to a radiographic imaging device and, in particular, to a radiographic imaging device equipped with a radiation detection panel.
2. Related Art
Flat panel detectors (FPDs) have become commercially viable in recent years. An FPD includes a radiation-sensitive layer that is placed on a thin film transistor (TFT) active matrix substrate, and the FPD detects incident radiation such as x-rays, directly converts the detected radiation into radiographic image data representing the distribution of the incident radiation amount, and then outputs the data. Portable radiographic imaging devices (also referred to below as electronic cassettes) have also become commercially viable. These devices incorporate a control unit that includes an image memory and a panel-type radiation detector such as an FPD, and a power source unit, and store radiographic image data output from the radiation detector in the image memory. Since an electronic cassette has excellent portability, a subject can be imaged while remaining on a stretcher or a bed and, in addition, since it is easy to adjust the imaging region by changing the position of the electronic cassette, it is possible to flexibly deal with situations where an immobile subject is to be imaged.
Related to the foregoing, Japanese Patent Application Laid-open (JP-A) No. 2003-339687 discloses a technique in which, in an imaging device such as an electronic cassette having a planar sensor, two planar sensors are joined along one of each of their edges in an openable and closable configuration, in order to increase the surface area of the planar sensor while also maintaining both portability and storability, and to realize imaging from plural directions.
JP-A No. 2004-173908 discloses a technique in which, in order to reduce the physical load on the operator, the electronic cassette (imaging unit) is separated from the imaging control unit and is set into a stage of an auxiliary device that is in a vertical state and, at the time of imaging, the stage (the detection surface of the electronic cassette) is raised to an horizontal state by operating an hydraulic cylinder that is connected to the stage.
JP-A No. 2009-80103 discloses a technique in which, in order to reduce the weight of a cassette system, a control unit equipped with electronic parts such as an interface circuit portion, a cassette control portion and a communications unit, is configured such that it can be disposed separately from the cassette holding the radiation detector via a connector and a cable, and the control unit is separated from the cassette at the time of imaging.
JP-A No. 2000-10220 discloses an x-ray imaging device having a configuration in which a panel case provided with an x-ray image detection means and a control case provided with a control means are connected to each other so as to be freely rotatable, with the aims of reducing size and thickness and of protecting the x-ray image detection means during transport and storage.
A radiographic imaging device such as an electronic cassette is configured such that the control unit and the power source unit in particular include a large number of electronic parts, and certain portions use electronic parts that give off a large amount of heat. As a result, there are cases when phenomena such as changes in the electrical properties of the radiation detector (for example, an increase in noise or an increase in TFT dark current) or deterioration of the radiation detector. A patient may become uncomfortable by an excessive increase in the surface temperature of a radiographic imaging device. In particular, when capturing a moving image by radiography, fluoroscopy or the like, since a greater amount of heat is produced as compared with a still image due to the continuous (long-term) image capture that is conducted, the above-mentioned phenomena are exacerbated and it may be necessary to devise measures, such as limiting the time of continuous operation, that may ultimately reduce the ease of use of the device.
In addition, examples of deterioration of a radiation detector include deformation or breakage caused by differences in the thermal expansion coefficient of respective members in a radiation detector having a layered structure and deterioration or separation of an adhesive caused by repeated temperature change. Further, when a radiation detector has a configuration that includes amorphous selenium, crystallization of the amorphous selenium may occur in conjunction with temperature increase in the radiation detector. Further, when a radiation detector has a configuration that includes a scintillator layer formed from CsI, the sensitivity of radiation detection may decrease in conjunction with temperature increase. The sensitivity of CsI changes at a sensitivity change rate of approximately 0.3% per 1° C. of temperature change, for example. As a result, since there is a high degree of temperature change when, for example, capturing a moving image by radiography, fluoroscopy or the like, which causes a large change in sensitivity, there is a large difference between the density of images captured toward the beginning of the period of image capture and images captured toward the end of the image capture period, which creates the possibility of problems such as deterioration in the visibility of moving images and reduced accuracy of diagnoses from moving images.
In this regard, the above-mentioned JP-A No. 2009-80103 proposes providing a means for cooling the radiation detector inside the cassette in order to suppress structural changes (crystallization) in the amorphous selenium that forms a part of the radiation detector. However, this is problematic in that the configuration of the radiographic imaging device becomes complicated and the installation of the cooling means may lead to an increase in the amount of power consumed by the radiographic imaging device. Further, the techniques described in JP-A Nos. 2003-339687, 2004-173908 and 2000-10220 give no consideration to heat dissipation or cooling.